Graphene is a single sheet or plural sheets taken out from graphite, and has an ideal two-dimensional structure constituted by sp2 carbon. Graphene is referred to as single layer graphene, two-layer graphene, multi-layer graphene, and the like, depending on the number of layers.
Graphene has been reported to have a considerably high mobility of electrons and holes (from 10,000 to 200,000 cm2/Vs), and the mobility exceeds silicon, GaAs and the like. Graphene is in the form of a two-dimensional sheet and thus can be applied with production techniques for semiconductors, such as lithography and etching, thereby providing various structures. Furthermore, graphene has excellent transparency and mechanical flexibility, and possibly has applications to various devices including a flexible transistor and a transparent electrode.
For providing a graphene sheet, a method of mechanically exfoliated from graphite, such as HOPG, with a Scotch adhesive tape has been practiced, but resulting graphene sheets are fluctuated in size and thickness, and cannot be subjected to practical applications.
As an alternative method therefor, formation of a graphene sheet by thermal decomposition of SiC, carbonization reaction on a single metal crystal in high vacuum, and the like have been reported. However, there are problems that the SiC single crystal substrate and an Ni (111) single crystal substrate used in these methods are expensive, and are available only in a limited size.
Under the circumstances, as a method of synthesizing graphene with a large area at low cost, a technique of performing carbonization reaction on a transition metal film by a chemical vapor deposition (CVD) method is proposed in recent years (see Non-patent Documents 1 to 3 and Patent Documents 1 and 2).